1. Field of the Invention
This invention relates to a control apparatus and more particularly to an apparatus for developing a non-oscillating torque to control the movement of a movable member, such as a gyroscope rotor, in a non-oscillatory manner.
2. Description of the Prior Art
There are several different types of prior art systems or apparatuses for producing torque. A pulse-on-demand prior art system only applies pulses of power to a torque producing means, such as a torque generator (torquer), gyro or the like, when it is desired to obtain a torque. Because such pulses of power may be randomly produced, this pulse-on-demand system fails to satisfy some basic requirements for the generation of precision torque. These requirements call for (1) a constant torquer current magnitude, and hence constant power dissipation, so that torquer temperature remains constant, and (2) a constant current load on the torque driver so that precision regulation is possible.
The above basic requirements are met in the systems taught in U.S. Pat. No. 3,354,366 (Landy, Jr. et al), and 3,403,316 (Conant, Jr.) by alternately passing constant amplitude positive and negative pulses through the coil of a torquer. Even when the torquer is at or near a null position, alternate positive and negative pulses are applied to the coil of the torquer. These basic requirements are also met in existing systems which utilize two coils (or some even multiple of two coils) on the torquer by supplying constant magnitude pulses to the torquer. In this case torque is controlled by selecting a positive torque coil or a negative torque coil as required, with zero torque being the alternate selection of the positive and negative torque coils. However, each of these above-described systems, which satisfy the basic requirements for generating a precision torque, develops an oscillating torque even when a zero or non-zero torque is desired. Hence, in each of these systems, the implementation for driving the torquers has the disadvantage of gnerating stable platform oscillation at torque rates near zero. In a three axis inertial system such oscillation may also cause unacceptable platform drift.
None of the above-described systems teaches an apparatus which not only satisfies the above-noted basic requirements for generating a precision torque but also develops a zero or non-zero torque without any oscillating component in that torque.